Impedance-equalizer for use with transformers



R. S. HOYT. IMPEDANCE EQUALIZER FCR USE WITH TRANSFORMERS. APPLICATION FILED JAN.17, 1918.

1,333, 1 1 1 I Patented Mar. 9, 1920 IN V EN TOR.

B Ray 5H0yt 'ATTORNLWS.

of a transformer and so proportioned with.

RAY S. HOYT,

0F BROOKLYN, NEW YORK, AssIGNoR TELEGRAPH COMPANY, A CORPORATION or NEW YORK.

T0 AMERICAN TELEPHONE Ann IMPEDANCE-EQUALIZER FOR USE WITH-TRANSFORMERS.

Specification of Letters Patent.

A Patented Mar. 9, 1920.

Application filed January 17, 1918. Serial No. 212,290.

To all whom it may concern:

Be it known that I, RAY S. HoY'r, residin at Brooklyn, in the county of Kings and State of New York, have invented certain Improvements in Impedance-Equalizers for Use with Transformers, of which the following is a specification.

This invention relates to an electrical transformer and more particularly it relates to the combination with a transformer of means for rendering the impedance of the primary circuit independent of the frequency and equal to the impedance of the secondary circuit multiplied by the transformer ratio.

It is well known to those acquainted with the art of telephony that the, proper functioning of a transmission system depends very strictly on the proper relative proportioning of the component elements of the system as regards their electrical impedances. Thus, a receiving station absorbs without reflection all the energy transmitted thereto by a transmission line when and only when the impedance of the receivin is equal to the characteristic impedance of the line. It is therefore important to proportion the' impedance of the receiving station relatively to the line impedance. Proper relative pro ortioning of the impedances .is particular y import-ant in connection with two-way repeater organizations because the impedance of the actual line must be as closely as possible equal to the im edance of the line which it balances.

n case it is impossible or inconvenient to make the actual impedances of the associated elements equal, their apparent impedances may be rendered approximately equal by replacing one element by the primary of a transformer of definite prearranged transformer ratio, and connecting said element across the secondary of the transformer. The impedance measured across the tenninals of the transformer primary is then roughly equal to the impedance of the element multiplied by the transformer ratio. This relation is, however, only approximate and only very roughly so unless the self impedances of primary and secondary are very large and the coupling very close.

In the resent invention impedance elements are inserted in series with the primary station reference to the transformer ratio and the impedance connected across the secondary terminals of the transformer that the resultant impedance of the' primary circuit is equal to the secondary impedance multiplied by the transformer ratio.

The invention is best understood by reference to the accompanying drawing, which is a diagram of the arrangement of my inventlon.

Referring to said drawing, a transformer is shown with an impedance 2 connected across the terminals 3, 3 of the secondary 4. Impedance 2 is conventionally represented as a non-inductive resistance and will be regarded as a resistance of value R in the subsequent explanation of the operation of my invention. In series with the primary 5 is connected an impedance 6 comprising a condenser 7 in parallel with a non-lnductive resistance 8.

In order to explain the nature of my invention and in particular to reduce the proper proportioning of condenser 7 and resistance 8 the ordinary formulaefor the impedance measured across the terminals 9, 9 and 10, 10 will now be given.

If Z denotes the impedance across terminals 9, 9; L and L the self inductances of primary 5 and secondary 4 respectively; M the mutual inductance between said coils; R the resistance of impedance element 2; p the frequency multiplied by '21:; and z' the imaginary operator T1 in accordance with standard notation, then Z is expressible as:

can be made negligibly small. This simply means, as is well known, that the coupling is ractlcally unity, that is, the magnetic lea age negligibly small. It is therefore per missible to Write instead of the rigorous formula mula:

men

(1), the following approximate forwhich by rationalization of the denominator -becomes:

' Now let Z' denote the impedance of the com bination 6; C. the capacity of condenser 7; and R the resistance of resistance 8. Then the value of Z is expressible as:

By rationalizationof the denominator formula "(4) becomes: n

p n-111 W W Comparison of (3) and (5) shows that if we to the product R0 the value R i the denominators of (5) and (3) become .30 equal, and the resultant impedance across terminals 10, is given by 1 F -F711 ZPE itt) The terms with the factor :5 in the numerator cancel out provided 4 I a I,

If then this value is assigned to R, equation (7) reducesto is the transformer ratio and R is the impedance connected across the terminals of the secondary. Therefore the impedance 66 across the terminals 10, 1G is equal to the pedance element associated with the secondsecondary impedance multiplied by the transformer ratio, provided that Formulae (10) are therefore the design formulae in accordance with which the elements 7 1 d 8 are to be proportioned to attain the esired result.

.Gomparison.of the impedances expressed in formulae (2) and (9) shows that, whereas the impedance across terminals 9, 9 varies with the frequency, the impedance across terminals 10, 10 is independent of the frequency and equal to the resistance R multiplied by the transformer ratio.

It .will be seen that by means of this in- 35 vention the impedance of the primary circuit of a transformer may be rendered independent of the frequency and equal to the impedance of the secondary circuit multiplied by the transformer ratio. It will also be obvious that the general principles herein disclosed may be embodied in organizations a widely different from that disclosed without departing from the spirit of the invention as defined in the following claims.

, What is claimed'is: 1

1. In combination, a transformer comprising primary and secondary windings, an im pedane element associated with the secondary winding of the transformer, a transmission circuit associated with the primary winding of the transformer, and means associated with the primary circuit whereby the resultant impedance of the primary circuit is rendered substantially equal at all frequencies to the secondary impedance multiplied by the transformer ratio. j

2. In combination, a transformer comprising primary and secondary wind' an imary winding of the transformer, a transnnssion circuit associated with the primary winding of the transformer, and an 1mpedance element between said transmission circuit and transformer, said last mentioned pedanceelem'ent being so roportioned that the resultant im dance 0 the rimary circuit is substantial y equal at all uencies to the im dance of the secondary circuit multipli by the transformer ratio.

3. An arrangement to associate circuits of unequal impedance comprising a transformer, and an impedance element in the primary circuit of the transformer so proportioned that the resultant impedance of the primary circuit is substantially. equal at all frequencies to the secondary impedance multiplied by the transformer ratio.

4; An arrangement to associate circuits of unequal impedance comprising a trans- 180 former, and an impedance element in the primary circuit of the transformer. so proportioned with reference to the transformer ratio and the impedance connected across the secondary terminals of the transformer that the resultant impedance of the rimary circuit is substantially equal at all equencies t0 the secondary impedance multiplied .by the transformer ratio.

5. An arrangement to associate circuits of unequal impedance comprising a transformer, and an impedance element in series with the primary winding of the transformer comprising a resistance'and capacity in parallel, said resistance and capacity being so proportioned that the resultant impedance of one circuit is rendered substan- 6. In combination, a transformer compris mg primary and secondary windings, circuits associated with each of saidwindings, and means associated with one of said windings whereby the resultant impedance of one of said circuits is rendered substantially equal at all frequencies to the impedance of the other circuit multiplied by the transformer ratio.

In testimony whereof, I have signed my name to this specification this 15th day of January, 1918.

RAY S. HOYT 

